Vehicular steering wheel assemblies typically comprise a centrally disposed nonrotatable steering column and a rotatable steering wheel. A rotatable shaft extends centrally through the steering column to enable the movements of the steering wheel to be transmitted appropriately to the wheels on which the vehicle is supported.
Virtually all vehicles require electrical connections to be made between the stationary steering column and the rotatable steering wheel. For example, electrical circuits extending from the nonrotatable steering column to the rotatable steering wheel may relate to the horn, driver-side emergency air bags and electrical accessories that may have primary or redundant controls mounted on the hub of the steering wheel.
The typical prior art electrical connections for steering wheel assemblies include opposed plates mounted respectively on the stationary column or rotatable steering wheel with flat flexible cables extending therebetween. This prior art assembly might include thirty feet of flat flexible cable wound in a clock spring manner. Opposed ends of the flat flexible cables are terminated to electrical connectors, which in turn are mounted to the opposed plates on the stationary steering column or rotatable steering wheel. These prior art assemblies with flat flexible cables extending between the stationary steering column and the rotatable steering wheel have a very high relative cost because of the large number of components and the large amount of flat flexible cable required. Additionally, it is extremely difficult to assemble the prior art components in a manner that ensures relatively free movement of the rotatable steering wheel without overstressing of the flat flexible cable at any location throughout the movement. These prior art assemblies relying on flat flexible cables have also prevented the use of a steering wheel assembly that could undergo unlimited free rotation relative to the stationary steering column. Thus, to prevent overstress on the flat flexible cable it is necessary to provide these prior art structures with appropriate means for preventing excessive rotation of the steering assembly relative to the stationary steering column. Even if these prior art assemblies can be properly assembled by original equipment manufacturers, there can be no assurance that automobile mechanics performing routine maintenance and repairs will achieve proper reassembly. It has also been found that the flat flexible cables will cause an audibly noticeable "cable slap" during normal rotation of the steering wheel. In some instances, a separate sound insulation has been required to attenuate the "cable slap" noises.
The prior art has included attempts to overcome the above described deficiencies of steering wheel assemblies employing flat flexible cable. In general these prior art attempts include opposed annular rings of conductive material nonrigidly mounted respectively to nonconductive portions of the stationary steering column and the rotatable steering wheel. The mounting of the rings has required complex means for permitting a controlled axial movement of the rings relative to the respective steering column and steering wheel. The prior art structures have further included complex biasing means for urging the annular electrically conductive rings toward one another and away from the respective steering column and steering wheel. The electrically conductive rings of the prior art structure are formed with annular channels having generally semicircular cross sections. Rigid metallic ball bearings are disposed in the channel between the annular nonrigidly mounted electrically conductive rings of the prior art structure to provide electrical connection between the rings. The contact against the rigid metallic ball bearings is achieved by the complex biasing means which urge the rings toward the rigid ball bearings. At least three or more ball bearings typically are provided for each pair of annular rings, with the prior art assembly typically being provided with complex means for controlling the circumferential position of the rigid ball bearings relative to one another to ensure that the ball bearings do not all roll together at a single location relative to the annular electrically conductive rings. Examples of assemblies of this general type are shown in U.S. Pat. No. 4,548,454 which issued to Zeller et al. on Oct. 22, 1985; U.S. Pat. No. 4,462,648 which issued to Fohl on July 31, 1984; and U.S. Pat. No. 4,475,779 which issued to Fohl on Oct. 9, 1984. Although this prior art avoids the use of flat flexible cables, the resulting structure with axially movable electrically conductive rings, springs to axially move the rings, electrical connections to the movable rings, rigid ball bearings between the rings and means for controlling the location of the ball bearings all are extremely complex and expensive.
Other prior art steering wheel assemblies include an apparatus having complexly configured annular contacts which are incorporated concentrically in interfitting electrical contact. These complexly configured rings are maintained in electrical contact by a plurality of coil springs aligned such that the longitudinal axes of the coil springs are parallel to the longitudinal axis of the steering column to urge the complexly configured electrically conductive rings in axial directions and into electrical contact with one another. The complexly configured rings are extremely expensive to manufacture, and the entire assembly is costly and undesirably complex. A device of this type is shown in U.S. Pat. No. 4,714,430 which issued to Zeller on Dec. 22, 1987.
The above described attempts to avoid flat flexible cable sometimes have replaced the "cable slap" noise with audibly distinct clicking caused by the complex interengagement of parts.
The complexities of all of the above described prior art substantially prevent increases in circuit density without corresponding increases in at least the radial dimensions of the assemblies and the entire steering column.
Recent advances have been made in three-dimensional molded wiring board technology employing the discrete plating of electrically conductive materials to various nonconductive plastic structures. In particular, the electrically conductive materials have been selectively disposed on the plastic to define electrically conductive surface regions extending through a three-dimensional matrix to define discrete conductive tracks for incorporation into electrical circuits. This three-dimensional molding technology is currently available from Mint Pac and others.
In view of the above, it is an object of the subject invention to provide improved electrical connections for steering wheel assemblies.
It is another object of the subject invention to provide electrical connections for steering wheel assemblies that can be manufactured easily and inexpensively, and that can be efficiently assembled.
Another object of the subject invention is to provide electrical connections between stationary and rotatable objects that avoid the use of cables and that employ a substantially minimum number of components.
Still a further object of the subject invention is to provide improved electrical connections between stationary and rotatable objects that can be efficiently environmentally sealed.
Yet another object of the subject invention is to provide efficient electrical connection between stationary and rotatable objects, such as in a steering wheel assembly, which insures redundant high quality electrical connection for all relative rotational orientations.
An additional object of the subject invention is to provide greater circuit density for electrical connection between a stationary steering column and a rotatable steering wheel, thereby enabling more electrical controls on the steering wheel.
Another object of the subject invention is to provide for continuous unlimited bidirectional rotation in an electrical connection between a steering column and a steering wheel.
Still another object of the subject invention is to provide a substantially noise-free electrical connection between a steering column and a steering wheel.